Velocity Synchrosqueezing Windowed Fourier Transform for Fault Diagnosis of Fixed-Shaft Gearbox Under Nonstationary Conditions

The Velocity synchrosqueezing transform (VST) is a good method to analyze the vibration signal for condition monitoring of planetary gearbox under non-stationary conditions. The VST is realized by jointly applying domain mapping, synchrosqueezing transform (SST) and time-frequency representation (TFR) restoration. It features a smear-free result for time-frequency analysis. However the VST has lower frequency resolution in the higher frequency region, this drawback limits its effectiveness in analyzing the vibration signal of fixed-shaft gearbox. To resolve this problem, this paper proposes the velocity synchrosqueezing windowed Fourier transform (VSWFT) method. Compared with the VST, this method employs the synchrosqueezing windowed Fourier transform (SWFT), instead of the SST, to process the angle-domain signal. As the SWFT uses window with fixed window length, it has fixed time-frequency resolution, which is more suitable for analyzing vibration signal of fixed-shaft gearbox. Finally the TFR is restored from the SWFT. The fault, if any, can be diagnosed by identifying the revealed sidebands of meshing frequency in the TFR. The effectiveness of the proposed method is validated using experimental vibration signal collected from a faulty gearbox under a non-stationary condition.